ATM kinase is a serine threonine kinase originally identified as the product of the gene mutated in ataxia telangiectasia. Ataxia telangiectasia is located on human chromosome 11q22-23 and codes for a large protein of about 350 kDa, which is characterized by the presence of a phosphatidylinositol (“PI”) 3-kinase-like serine/threonine kinase domain flanked by FRAP-ATM-TRRAP and FATC domains which modulate ATM kinase activity and function. ATM kinase has been identified as a major player of the DNA damage response elicited by double strand breaks. It primarily functions in S/G2/M cell cycle transitions and at collapsed replication forks to initiate cell cycle checkpoints, chromatin modification, HR repair and pro-survival signalling cascades in order to maintain cell integrity after DNA damage (Lavin, M. F.; Rev. Mol. Cell Biol. 2008, 759-769).
ATM kinase signalling can be broadly divided into two categories: a canonical pathway, which signals together with the Mre11-Rad50-NBS1 complex from double strand breaks and activates the DNA damage checkpoint, and several non-canonical modes of activation, which are activated by other forms of cellular stress (Cremona et al., Oncogene 2013, 3351-3360).
ATM kinase is rapidly and robustly activated in response to double strand breaks and is reportedly able to phosphorylate in excess of 800 substrates (Matsuoka et al., Science 2007, 1160-1166), coordinating multiple stress response pathways (Kurz and Lees Miller, DNA Repair 2004, 889-900). ATM kinase is present predominantly in the nucleus of the cell in an inactive homodimeric form but autophosphorylates itself on Ser1981 upon sensing a DNA double strand break (canonical pathway), leading to dissociation to a monomer with full kinase activity (Bakkenist et al., Nature 2003, 499-506). This is a critical activation event, and ATM phospho-Ser1981 is therefore both a direct pharmacodynamic and patient selection biomarker for tumour pathway dependency.
ATM kinase responds to direct double strand breaks caused by common anti-cancer treatments such as ionising radiation and topoisomerase-II inhibitors (doxorubicin, etoposide) but also to topoisomerase-I inhibitors (for example irinotecan and topotecan) via single strand break to double strand break conversion during replication. ATM kinase inhibition can potentiate the activity of any these agents, and as a result ATM kinase inhibitors are expected to be of use in the treatment of cancer.
CN10237271 IA reports certain imidazo[4,5-c]quinolin-2-one compounds which are mentioned to be dual inhibitors of PI 3-kinase α and mammalian target of rapamycin (“mTOR”) kinase. Among the compounds reported in CN10237271 IA are the following:
